The pollination of crops by bees is responsible for a third of the food produced in the US.

One in every three mouthfuls has been touched by their tiny feet; but our six-legged friends are in trouble.

They are getting sick and leaving their hives. Without bees, food gets more expensive - some products could disappear altogether.

Colony collapse disorder (CCD) emerged last year, and by spring 2007 bees were dying in huge numbers - over the year as a whole the total bee population fell by 30%.

Some beekeepers lost closer to 90%, and the fear is it will get worse.

Beekeeper Gilly Sherman says: "It's worse than last year, and last year was worse than the year before, so it's bad, and there are a lot of good big beekeepers that are having a lot of problems.

"I think we're coming in for a big train wreck."

Few answers

He has moved his bees to Bakersfield, California. The state's Central Valley is home to the largest managed pollination event in the world - 1.5 million hives are transported there on trucks.

That is almost every commercial hive in the country. Without bees there would be practically no almonds, and it's the same for many other crops. Apples, strawberries, even onions, all depend on bees.

Bees are frozen to preserve them for research

Yet despite their importance, there is still no answer to the problem of CCD.

Its causes remain a mystery even after a year of intense publicity.

Part of that is due to lack of funding, say researchers, who rejoiced at the news that Haagen-Dazs, the ice cream maker, is donating $250,000 to their cause.

At Penn State University, nestled in the Pennsylvania countryside, scientists spend day and night working on the problem.

Bees are collected and kept at freezing temperatures to preserve them so they can be ground down to show up viruses, bacteria and other pathogens - basically anything that causes disease.

Many different types have been found, so it is proving difficult to know what the main cause is. A parasite called Nosema ceranae, which infects the bee's guts, has been found too.

Raj Singh, who made one of the most recent discoveries, says: "We have found some of the honey bees that are uninfected bringing in pollen pellets from the field, and those pollen pellets were actually infected - that's one of the routes of virus transmission that we've found."

But he admits they are far from finding the "silver bullet" and even further from knowing how to stop it.

Limited funds

Entomologist at Penn State, Diana Cox Foster, says it is an urgent problem.

"We do feel that we need additional monies to come in for grants to work on this problem," she said. "We also need to have collaboration internationally to address what the role of different pathogens is."

Beekeeper Gilly Sherman is moving his hives

She acknowledged that a quarter of a million dollars from Haagen-Dazs isn't much when faced with such a mysterious problem, but says better offers from higher authorities are few and far between.

"At the Senate and at the House of Representatives, at the federal level, they have said that they are quite interested and they would like to help a great deal but we haven't yet seen the monies being released for this.

"It is of concern, and hopefully other people will start to see it that way before it hits us in the supermarkets."

Bees' influence on supermarket shelves is vast. As well as fruits and vegetables, it could get as far as beef and dairy products because cows are fed alfalfa - another bee-pollinated plant.

Of course honey would disappear altogether without bees. More money and more commitment to research are called for to keep this essential industry going.

In a world so dominated by man it may come as a big shock to realise there are some things we cannot do without nature's help.